2 files changed, 335 insertions, 0 deletions

diff --git a/crates/hir_def/src/path/lower.rs b/crates/hir_def/src/path/lower.rs
new file mode 100644
index 000000000..07b9723ce
--- /dev/null
+++ b/crates/hir_def/src/path/lower.rs
@@ -0,0 +1,215 @@
+//! Transforms syntax into `Path` objects, ideally with accounting for hygiene
+
+mod lower_use;
+
+use std::sync::Arc;
+
+use either::Either;
+use hir_expand::{
+    hygiene::Hygiene,
+    name::{name, AsName},
+};
+use syntax::ast::{self, AstNode, TypeBoundsOwner};
+
+use super::AssociatedTypeBinding;
+use crate::{
+    body::LowerCtx,
+    path::{GenericArg, GenericArgs, ModPath, Path, PathKind},
+    type_ref::{TypeBound, TypeRef},
+};
+
+pub(super) use lower_use::lower_use_tree;
+
+/// Converts an `ast::Path` to `Path`. Works with use trees.
+/// It correctly handles `$crate` based path from macro call.
+pub(super) fn lower_path(mut path: ast::Path, hygiene: &Hygiene) -> Option<Path> {
+    let mut kind = PathKind::Plain;
+    let mut type_anchor = None;
+    let mut segments = Vec::new();
+    let mut generic_args = Vec::new();
+    let ctx = LowerCtx::with_hygiene(hygiene);
+    loop {
+        let segment = path.segment()?;
+
+        if segment.coloncolon_token().is_some() {
+            kind = PathKind::Abs;
+        }
+
+        match segment.kind()? {
+            ast::PathSegmentKind::Name(name_ref) => {
+                // FIXME: this should just return name
+                match hygiene.name_ref_to_name(name_ref) {
+                    Either::Left(name) => {
+                        let args = segment
+                            .generic_arg_list()
+                            .and_then(|it| lower_generic_args(&ctx, it))
+                            .or_else(|| {
+                                lower_generic_args_from_fn_path(
+                                    &ctx,
+                                    segment.param_list(),
+                                    segment.ret_type(),
+                                )
+                            })
+                            .map(Arc::new);
+                        segments.push(name);
+                        generic_args.push(args)
+                    }
+                    Either::Right(crate_id) => {
+                        kind = PathKind::DollarCrate(crate_id);
+                        break;
+                    }
+                }
+            }
+            ast::PathSegmentKind::Type { type_ref, trait_ref } => {
+                assert!(path.qualifier().is_none()); // this can only occur at the first segment
+
+                let self_type = TypeRef::from_ast(&ctx, type_ref?);
+
+                match trait_ref {
+                    // <T>::foo
+                    None => {
+                        type_anchor = Some(Box::new(self_type));
+                        kind = PathKind::Plain;
+                    }
+                    // <T as Trait<A>>::Foo desugars to Trait<Self=T, A>::Foo
+                    Some(trait_ref) => {
+                        let path = Path::from_src(trait_ref.path()?, hygiene)?;
+                        kind = path.mod_path.kind;
+
+                        let mut prefix_segments = path.mod_path.segments;
+                        prefix_segments.reverse();
+                        segments.extend(prefix_segments);
+
+                        let mut prefix_args = path.generic_args;
+                        prefix_args.reverse();
+                        generic_args.extend(prefix_args);
+
+                        // Insert the type reference (T in the above example) as Self parameter for the trait
+                        let last_segment = generic_args.last_mut()?;
+                        if last_segment.is_none() {
+                            *last_segment = Some(Arc::new(GenericArgs::empty()));
+                        };
+                        let args = last_segment.as_mut().unwrap();
+                        let mut args_inner = Arc::make_mut(args);
+                        args_inner.has_self_type = true;
+                        args_inner.args.insert(0, GenericArg::Type(self_type));
+                    }
+                }
+            }
+            ast::PathSegmentKind::CrateKw => {
+                kind = PathKind::Crate;
+                break;
+            }
+            ast::PathSegmentKind::SelfKw => {
+                kind = PathKind::Super(0);
+                break;
+            }
+            ast::PathSegmentKind::SuperKw => {
+                let nested_super_count = if let PathKind::Super(n) = kind { n } else { 0 };
+                kind = PathKind::Super(nested_super_count + 1);
+            }
+        }
+        path = match qualifier(&path) {
+            Some(it) => it,
+            None => break,
+        };
+    }
+    segments.reverse();
+    generic_args.reverse();
+
+    // handle local_inner_macros :
+    // Basically, even in rustc it is quite hacky:
+    // https://github.com/rust-lang/rust/blob/614f273e9388ddd7804d5cbc80b8865068a3744e/src/librustc_resolve/macros.rs#L456
+    // We follow what it did anyway :)
+    if segments.len() == 1 && kind == PathKind::Plain {
+        if let Some(macro_call) = path.syntax().parent().and_then(ast::MacroCall::cast) {
+            if macro_call.is_bang() {
+                if let Some(crate_id) = hygiene.local_inner_macros() {
+                    kind = PathKind::DollarCrate(crate_id);
+                }
+            }
+        }
+    }
+
+    let mod_path = ModPath { kind, segments };
+    return Some(Path { type_anchor, mod_path, generic_args });
+
+    fn qualifier(path: &ast::Path) -> Option<ast::Path> {
+        if let Some(q) = path.qualifier() {
+            return Some(q);
+        }
+        // FIXME: this bottom up traversal is not too precise.
+        // Should we handle do a top-down analysis, recording results?
+        let use_tree_list = path.syntax().ancestors().find_map(ast::UseTreeList::cast)?;
+        let use_tree = use_tree_list.parent_use_tree();
+        use_tree.path()
+    }
+}
+
+pub(super) fn lower_generic_args(
+    lower_ctx: &LowerCtx,
+    node: ast::GenericArgList,
+) -> Option<GenericArgs> {
+    let mut args = Vec::new();
+    let mut bindings = Vec::new();
+    for generic_arg in node.generic_args() {
+        match generic_arg {
+            ast::GenericArg::TypeArg(type_arg) => {
+                let type_ref = TypeRef::from_ast_opt(lower_ctx, type_arg.ty());
+                args.push(GenericArg::Type(type_ref));
+            }
+            ast::GenericArg::AssocTypeArg(assoc_type_arg) => {
+                if let Some(name_ref) = assoc_type_arg.name_ref() {
+                    let name = name_ref.as_name();
+                    let type_ref = assoc_type_arg.ty().map(|it| TypeRef::from_ast(lower_ctx, it));
+                    let bounds = if let Some(l) = assoc_type_arg.type_bound_list() {
+                        l.bounds().map(|it| TypeBound::from_ast(lower_ctx, it)).collect()
+                    } else {
+                        Vec::new()
+                    };
+                    bindings.push(AssociatedTypeBinding { name, type_ref, bounds });
+                }
+            }
+            // Lifetimes and constants are ignored for now.
+            ast::GenericArg::LifetimeArg(_) | ast::GenericArg::ConstArg(_) => (),
+        }
+    }
+
+    if args.is_empty() && bindings.is_empty() {
+        return None;
+    }
+    Some(GenericArgs { args, has_self_type: false, bindings })
+}
+
+/// Collect `GenericArgs` from the parts of a fn-like path, i.e. `Fn(X, Y)
+/// -> Z` (which desugars to `Fn<(X, Y), Output=Z>`).
+fn lower_generic_args_from_fn_path(
+    ctx: &LowerCtx,
+    params: Option<ast::ParamList>,
+    ret_type: Option<ast::RetType>,
+) -> Option<GenericArgs> {
+    let mut args = Vec::new();
+    let mut bindings = Vec::new();
+    if let Some(params) = params {
+        let mut param_types = Vec::new();
+        for param in params.params() {
+            let type_ref = TypeRef::from_ast_opt(&ctx, param.ty());
+            param_types.push(type_ref);
+        }
+        let arg = GenericArg::Type(TypeRef::Tuple(param_types));
+        args.push(arg);
+    }
+    if let Some(ret_type) = ret_type {
+        let type_ref = TypeRef::from_ast_opt(&ctx, ret_type.ty());
+        bindings.push(AssociatedTypeBinding {
+            name: name![Output],
+            type_ref: Some(type_ref),
+            bounds: Vec::new(),
+        });
+    }
+    if args.is_empty() && bindings.is_empty() {
+        None
+    } else {
+        Some(GenericArgs { args, has_self_type: false, bindings })
+    }
+}
diff --git a/crates/hir_def/src/path/lower/lower_use.rs b/crates/hir_def/src/path/lower/lower_use.rs
new file mode 100644
index 000000000..53cecb05f
--- /dev/null
+++ b/crates/hir_def/src/path/lower/lower_use.rs
@@ -0,0 +1,120 @@
+//! Lowers a single complex use like `use foo::{bar, baz};` into a list of paths like
+//! `foo::bar`, `foo::baz`;
+
+use std::iter;
+
+use either::Either;
+use hir_expand::{hygiene::Hygiene, name::AsName};
+use syntax::ast::{self, NameOwner};
+use test_utils::mark;
+
+use crate::path::{ImportAlias, ModPath, PathKind};
+
+pub(crate) fn lower_use_tree(
+    prefix: Option<ModPath>,
+    tree: ast::UseTree,
+    hygiene: &Hygiene,
+    cb: &mut dyn FnMut(ModPath, &ast::UseTree, bool, Option<ImportAlias>),
+) {
+    if let Some(use_tree_list) = tree.use_tree_list() {
+        let prefix = match tree.path() {
+            // E.g. use something::{{{inner}}};
+            None => prefix,
+            // E.g. `use something::{inner}` (prefix is `None`, path is `something`)
+            // or `use something::{path::{inner::{innerer}}}` (prefix is `something::path`, path is `inner`)
+            Some(path) => match convert_path(prefix, path, hygiene) {
+                Some(it) => Some(it),
+                None => return, // FIXME: report errors somewhere
+            },
+        };
+        for child_tree in use_tree_list.use_trees() {
+            lower_use_tree(prefix.clone(), child_tree, hygiene, cb);
+        }
+    } else {
+        let alias = tree.rename().map(|a| {
+            a.name().map(|it| it.as_name()).map_or(ImportAlias::Underscore, ImportAlias::Alias)
+        });
+        let is_glob = tree.star_token().is_some();
+        if let Some(ast_path) = tree.path() {
+            // Handle self in a path.
+            // E.g. `use something::{self, <...>}`
+            if ast_path.qualifier().is_none() {
+                if let Some(segment) = ast_path.segment() {
+                    if segment.kind() == Some(ast::PathSegmentKind::SelfKw) {
+                        if let Some(prefix) = prefix {
+                            cb(prefix, &tree, false, alias);
+                            return;
+                        }
+                    }
+                }
+            }
+            if let Some(path) = convert_path(prefix, ast_path, hygiene) {
+                cb(path, &tree, is_glob, alias)
+            }
+        // FIXME: report errors somewhere
+        // We get here if we do
+        } else if is_glob {
+            mark::hit!(glob_enum_group);
+            if let Some(prefix) = prefix {
+                cb(prefix, &tree, is_glob, None)
+            }
+        }
+    }
+}
+
+fn convert_path(prefix: Option<ModPath>, path: ast::Path, hygiene: &Hygiene) -> Option<ModPath> {
+    let prefix = if let Some(qual) = path.qualifier() {
+        Some(convert_path(prefix, qual, hygiene)?)
+    } else {
+        prefix
+    };
+
+    let segment = path.segment()?;
+    let res = match segment.kind()? {
+        ast::PathSegmentKind::Name(name_ref) => {
+            match hygiene.name_ref_to_name(name_ref) {
+                Either::Left(name) => {
+                    // no type args in use
+                    let mut res = prefix.unwrap_or_else(|| ModPath {
+                        kind: PathKind::Plain,
+                        segments: Vec::with_capacity(1),
+                    });
+                    res.segments.push(name);
+                    res
+                }
+                Either::Right(crate_id) => {
+                    return Some(ModPath::from_segments(
+                        PathKind::DollarCrate(crate_id),
+                        iter::empty(),
+                    ))
+                }
+            }
+        }
+        ast::PathSegmentKind::CrateKw => {
+            if prefix.is_some() {
+                return None;
+            }
+            ModPath::from_segments(PathKind::Crate, iter::empty())
+        }
+        ast::PathSegmentKind::SelfKw => {
+            if prefix.is_some() {
+                return None;
+            }
+            ModPath::from_segments(PathKind::Super(0), iter::empty())
+        }
+        ast::PathSegmentKind::SuperKw => {
+            let nested_super_count = match prefix.map(|p| p.kind) {
+                Some(PathKind::Super(n)) => n,
+                Some(_) => return None,
+                None => 0,
+            };
+
+            ModPath::from_segments(PathKind::Super(nested_super_count + 1), iter::empty())
+        }
+        ast::PathSegmentKind::Type { .. } => {
+            // not allowed in imports
+            return None;
+        }
+    };
+    Some(res)
+}